The present invention relates to a composition and process for coloring hair. There are essentially two ways in which hair fibers may be dyed: “permanent” dyeing and “semi-permanent” dyeing.
The first, also known as oxidation dyeing, uses “oxidation” dye precursors, which are colorless or weakly colored compounds. Once mixed with oxidizing products, at the time of use, these precursors lead to colored compounds and dyes via a process of oxidative condensation. In this case, the colorations obtained are generally very colorfast and strong.
The second, also known as direct dyeing, uses direct dyes, which are nonionic or ionic dyes and colored compounds capable of producing a more or less pronounced change of the natural color of the hair, resistant to shampoo-washing several times. These dyes may or may not be used in the presence of an oxidizing agent.
In contrast with oxidation dye precursors, a direct dye is a relatively voluminous molecule that does not penetrate easily into the core of the fiber. Consequently, even though considerable progress has been made in this field, the phenomenon of bleeding of the coloration, i.e., color loss, during shampooing is still non-negligible, even if the dye(s) used is (are) chosen from cationic species. Moreover, the use of certain cationic direct dyes may be reflected by a reduction in the working qualities of the shampoos used after coloration, especially as regards the duration of the lather.
While the phenomenon of bleeding of the coloration during shampooing is more pronounced when direct dyes are used, this phenomenon occurs when oxidation dye precursors are employed as well.
Thus, one object of the present invention is to provide a composition and process for dyeing hair in a manner which inhibits color loss resulting from subsequent shampooing of the dyed hair fibers.